In a knife sharpening system in which a grinding member is rotated by a motor, rotation of the grinding member is achieved under the condition that RPM of the motor is reduced. Rotation of a polishing brush is also carried out under the above-mentioned conditions. For this reason, it is necessary to employ a reduction gear in a conventional knife sharpening system. As a result, there is a disadvantage in that relatively high power is required. To this end, such a knife sharpening system should be mounted in factories to which electricity can be supplied. Otherwise, a separate electric generator should be equipped to power the knife sharpening system. In particular, when such a knife sharpening system is mounted in a vehicle, to be movable, the electric generator is essentially necessary. However, such an electric generator not only generates severe noise, but also causes enlargement of the system. Due to the enlarged size of the knife sharpening system, it is difficult to mount the electric generator in a small vehicle.